There is a technology known in the related art whereby the extent of movement in the position of a projection image projected onto a projection target surface, attributable to a wobble at the projection device, is minimized by detecting the change in the attitude of the projection device (see patent reference 1). There are applications in the known art in which an optical image is projected onto a wall surface or the like (also see patent reference 1). In such applications, control is executed whenever the projection direction along which the projection device projects the image shifts so as to reduce the extent of shaking of the projection image on the projection target surface.    Patent reference 1: Japanese Laid Open Patent Publication No. 2006-138939